The invention relates to a system and method for automated treatment of chemical compounds or biological materials on solid supports, and more specifically, a system and method for automated purification, elution, cleavage, transfer, concentration and/or evaporation of biological or chemical samples on solid supports.
In recent years, the pharmaceuticals industry has devoted significant resources to finding ways to cut the time required for identification and validation of lead drug candidates. Disciplines that have arisen to address this need include high-throughput screening and combinatorial chemistry. Using combinatorial methods, libraries made up of large numbers of compounds are randomly or semi-randomly synthesized, then evaluated using high-throughput screening, looking for biological activity or chemical reactions. The availability of solid-phase supports, e.g., resin beads, balls, disks or tubes, for organic synthesis has contributed significantly to the ability to create large combinatorial libraries, making it possible to synthesize a unique compound on each support. Encoding of the solid support enables individual labeling of each compound and tracking of the compound""s reaction history. Examples of tagging and tracking techniques as described in U.S. Pat. Nos. 5,770,455 and 5,961,923, both assigned to the assignee of the present application, the disclosures of which are incorporated herein by reference. Such tagging and/or tracking capabilities permit discrete compound split-and-pool synthesis, allowing thousands to millions of compounds to be generated at a time while keeping track of the history of each uniquely synthesized compound throughout the synthesis and subsequent cleaving operations. However, while synthesis and tracking are facilitated by solid phase methods, analysis of the compound or its intermediates may, for many tests requires removal of the synthesized compounds from their solid phase carriers, such that individualized cleavage and concentration of each compound becomes essential. Furthermore, for generation of commercial libraries, it would be preferable to provide the compounds in a convenient form that would require the purchaser to do minimal additional processing in order to perform subsequent assays or other analyses, i.e., following cleaving from the solid support and concentration of the compound. Thus, automated cleavage, concentration and collection of the compounds in a manner that significantly reduces the bottleneck in an otherwise high-throughput process, which allows the compounds to be readily tracked, and which avoids loss of material or cross-contamination between compounds, is an important step in achieving the goals of rapid drug discovery and development.
Solid phase methods have similarly been applied for analysis of biological compounds. Generally, solid phase oligonucleotide synthesis involves covalently attaching the base building block to a solid support such as controlled pore glass (CPG), polystyrene-copolymer, polyester, silica gel, polyamide/Kieselguhr, charged nylon, glass fiber, nitrocellulose or cellulose paper, then synthesizing the oligonucleotide by placing the solid support in a reaction vessel with excess protected nucleosides and coupling reagents.
After completion, the oligonucleotide is cleaved from the solid support then deprotected, after which the appropriate analysis can be performed. Such methods have been adapted for purification of DNA, which typically involves the selective elution of impurities by exposing the biological sample to a number of reagents and incubating at elevated temperatures. The sample remains attached to the solid support throughout the purification steps then, if desired, the sample can be cleaved from the solid support. DNA purification procedures often require a combination of hazardous reagents, physical force (centrifuge, air pressure or vacuum), lengthy incubation periods and high temperatures (100xc2x0 C.), which can require special containers and equipment that may not be well suited for very high throughput operations. For example, see International Patent Application No. WO99/13976 of Gentra Systems, Inc., which discloses an automated apparatus for isolating DNA, in which biological samples are combined with solid supports in a sample processing container, wash solution is dispensed into the containers and drained a number of times, then the sample containers are loaded onto a purification apparatus, e.g., a centrifuge. After completion of the purification step, the sample processing container is removed and moved to the next station for cleavage (elution) of the purified sample from the solid support. Thus, while the method disclosed in the referenced PCT application is automated, there is still a significant amount of handling and moving of the samples and sample containers required to complete the purification and elution process.
Systems are known for performing cleavage, elution, concentration, purification, and/or collection of multiple samples, both chemical and biological, however, such systems are not easily integrated into a single processing system that enables the handling of a large number of samples to be cleaved, concentrated and collected automatically. For example, the centrifugal system for vacuum concentration of biological specimens disclosed in U.S. Pat. No. 5,334,130 enables treatment of multiple biological samples within the centrifuge chamber. Cleavage of the compounds from their supports is effected by pouring a typically caustic cleaving agent into each vial before placing the vials into the centrifuge chamber. The chamber is sealed and heated to accelerate cleavage. After cleavage is complete, the concentration step occurs during which the chamber is evacuated and the centrifuge rotor is activated to evaporate the cleaving agent. The rotor speed can sometimes be selected to minimize xe2x80x9cbumpingxe2x80x9d, which can cause solid or liquid form material to be propelled out of the vial due to violent outgassing caused by boiling of the solvent. In the system disclosed in the ""130 patent, the rotor has a number of holder positions, each of which includes a pressure relief valve for its corresponding vial, thus limiting the number of sample-containers, and consequently, the number of samples, to the number of holder position.
An important aspect of streamlining the process for synthesis, cleavage and concentration of compounds involves establishing a system that allows the compounds to be processed through multiple process steps without frequent transfer of the solid supports and/or compounds from one container to another as needed to allow a certain piece of equipment to be used. However, in the described systems, unless prior processing steps were also performed in the sample containers, transfer into such containers would be required before the cleavage and concentration procedure could be performed. Thus, the cleavage/concentration steps would become rate-limiting in a high-throughput process for several reasons which include: (1) additional handling of the samples is required to place them in the containers; (2) the often-hazardous cleavage agent must be introduced into the container, then the container carefully carried to the centrifuge chamber for loading; and (3) the cleavage and concentration steps are performed as separate procedures.
For the reasons described above, there remains a need for a system for processing of samples on solid supports, which may include cleavage, transfer/collection and/or concentration, that allows for a highly automated method of reagent delivery, cleaving, transfer and/or concentration of a large number of chemical or biological samples in a rapid, cost effective manner.
It is an advantage of the present invention to provide a system that automatically dispenses one or more liquid solutions within a centrifuge for simultaneous treatment of a number of chemical or biological samples on solid supports.
It is another advantage of the present invention to provide a system and method for automatically sample washing, eluting, cleaving, concentrating and collecting a large number of samples on solid supports.
Still another advantage of the present invention is to permit treatment of chemical or biological samples in a sealed system which avoids the need for operator handling of hazardous solutions and permits a vacuum to be applied during processing.
It is a further advantage of the present invention to provide an automated system and method for processing of chemical or biological samples that allows the processing temperature to be accurately controlled to prevent heat damage to samples and containers.
Another advantage of the present invention is to provide an automated system that significantly minimizes the possibility of cross-contamination and/or loss of samples during processing.
Yet another advantage of the present invention is to provide an automated system that precisely measures and dispenses hazardous solutions during all processing operations in a sealed system.
In an exemplary embodiment, the automated processing system of the present invention comprises a computer-based control unit and a main unit comprising a variable-speed centrifuge having an openable vacuum-tight chamber and a centrifuge rotor with a plurality of multi-sample holding positions, a liquid solution supply subsystem which feeds solvent or other solution to a plurality of dispensing stations in the centrifuge chamber, a temperature control subsystem, and a vacuum subsystem. In the preferred embodiment bar code reader or other identification means, preferably a non-contact reader, can be included in the chamber to allow sample carriers to be identified.
Solid support-bound sample compounds are retained within a multi-well sample container which is mated on its lower end with a collection container possessing a collection well corresponding to each well of the sample container. When mated, the two containers are inserted into one of the multi-sample holding positions on the centrifuge rotor. After closing the centrifuge chamber, cleaving solvent (or other appropriate reagent) is automatically dispensed into each well of the sample container, with the centrifuge rotor being rotated to position each sample container at the dispensing station. By running the rotor at a low rotational speed while dispensing and during cleavage, potential carryover of solvent and/or samples (xe2x80x9ccreepxe2x80x9d) between the wells is significantly minimized. As the rotor turns, samples are allowed to incubate until the samples are cleaved from the solid supports. When cleaving is complete as pre-programmed based upon the sample types and, for chemical compounds, the linker types, the rotor speed is increased, causing the cleaved sample and solvent to be transferred to the collection container, leaving the solid support in the sample container. After all of the cleaved solutions are transferred into the collection containers, the rotor speed is increased to a relatively high rate. The collection containers are uniformly heated, causing the cleaving solvent to uniformly evaporate at a user-programmable rate. The vacuum within the chamber is controlled to accelerate the evaporation. After a pre-determined period of time, the process is terminated, leaving the concentrated samples in the bottoms of the wells of the collection containers.
In the preferred embodiment, the control unit comprises a PC with a Windows(copyright)-type operating system to provide a user-interface via mouse or keyboard. The PC includes a memory within which is stored software for controlling and monitoring the various subsystems within the cleavage/evaporation system. Where the cleavage/evaporation system is part of a processing system for synthesizing compounds, the memory will also preferably have stored therein software for management of the synthesis, including tracking of the encoded solid supports, the chemical building blocks used in the synthesis, and the concentrated sample compounds after cleavage. The control unit also includes power supplies, the main control relay, and a network bus controller. The power supplies provide power to the main unit and any operating device within the system that requires power for operation. The control unit includes a single connection to the main electrical supply, i.e., electrical outlet, thus providing for total system control through the control unit, allowing rapid shutdown of an individual subsystem, or the entire system, if required. The main switching unit provides switching of the devices of the main unit in response to commands issued by the PC according to the control software. The network bus controller provides data transfer (I/O) between the PC and the main unit for conveying control commands to the various devices and for receiving monitoring data from the system sensors. A conventional cable provides physical connection between the control unit and the main unit.
The centrifuge chamber must be sufficiently sealed so that it is capable of maintaining a vacuum and is resistant to the harsh chemicals used during processing of the samples. In the preferred embodiment, sample holder positions are fixed on the centrifuge rotor, with a plurality of inwardly-sloping support frames or blocks radially mounted at evenly-spaced positions around the rotor. In an alternate embodiment, the sample holders are pivotally mounted to swing at an increasing angle as the rotor speed increased. Each support frame is adapted to receive the assembled combination of the sample container and collection container. The rotor has openings therethrough at locations corresponding to each support frame to permit heating of the collection container from below the rotor. The centrifuge chamber has a plurality of heat-transmissive windows formed in its bottom side. At least one light-transmissive window is formed in the side of the centrifuge chamber to provide access for optical reading of bar codes on the sample and collection containers. A second light-transmissive window may be formed in the top of the centrifuge chamber to permit optical transmission of a signal from a temperature sensor located inside the chamber.
The solvent supply subsystem includes at least one source container and pump which provide solvent to a dispensing station. In the preferred embodiment, two dispensing stations are included, each having its own source container and pump, so that two different solvents can be supplied. The dispensing station includes a dispensing head which is mounted on and extends into the centrifuge chamber in a manner which provides access to all wells in the sample container. The dispensing head has one dispensing tip or nipple corresponding to each well in the sample container and is arranged such that alignment of the dispensing head with the sample container causes each dispensing nipple to align with its corresponding well. Each dispensing tip is connected by a tube to a corresponding solvent reservoir in the dispenser housing. The solvent reservoir contains a pre-measured amount of solvent so that the precise amount of solvent used is known. The source supply subsystem also includes a waste reservoir for safe storage of used solvent and a gas source for purging the dispenser tubing and dispensing tip.
The temperature control subsystem includes temperature sensors and heating means. Heat to the samples is supplied via infrared heat lamps positioned outside of the bottom of the centrifuge chamber at the heat-transmissive windows. Conduction and uniform dispersion of the heat entering the windows is provided by heat-conducting plates disposed within the support frames on the rotor, beneath each of the collection containers. A thermal sensor in contact with one of the heat-conducting plates provides a signal to an optical (IR) transmitter located below the light-transmissive window in the top of the centrifuge chamber. The infrared signal is detected by a detector positioned outside of the light-transmissive window and a signal is generated to provide feedback to the sample heat controller for controlling the heat lamps. Additional heat to the chamber is provided by resistive heaters mounted on the centrifuge housing, preferably on both the top and bottom of the chamber. A sensor mounted on the outside of the chamber provides feedback for controlling the chamber temperature.
The vacuum subsystem includes a vacuum controller for controlling a pair of pumps, which in the preferred embodiment are a Roots pump and a diaphragm pump. A condenser may be included for removal of vaporized solvent from the evacuated air from the centrifuge chamber to prevent possible release of the solvent into the environment.
Tracking of the location of the sample compounds is enabled by identification of the sample and collection containers. In the preferred embodiment, each of the containers is marked with an optically-readable bar code. Orientation keys are included on the containers to ensure that the bar code is visible through the window in the side of the centrifuge chamber. The bar code reader reads the encoded identification and provides that information to the control unit (PC) which stores the information in association with the synthesis histories of the samples as provided by the synthesis management software. The samples in the sample and collection containers are tracked spatially, according to the coordinates of the wells in which they are placed. As an alternative to the optical bar code, radio frequency (RF), or other remotely-readable tags may be embedded in the containers to provide means for identifying and tracking the containers.